Numerous types of apparatus and processes that use heat to seal and/or seam thermoplastic, elastomeric, paper, and other materials are known in the art. For example, heat sealing is one such process that is used to weld material to itself along a seam or seal, or to join pieces of material together into larger pieces, such as, for example, tarps, tarpaulins, signs, tents, and inflatables. This process involves applying heat along a path on a surface(s) of a material to sufficiently melt a portion of the surface(s) along the path where a seal or seam is to be formed with the material, contacting the melted portion of the surface with either a corresponding melted surface or non-melted surface of the material, and then applying pressure along the heated surface of the material to facilitate seam or seal formation when the melted portion of the material solidifies.
One common implementation of heat sealing involves a direct contact method. This method involves contacting a constantly heated die or sealing bar to a specific contact area or path along surfaces of thermoplastic or elastomeric materials to be sealed or seamed together. In some sealing and seaming operations, thermoset adhesives are applied along the contact area or path and, once activated, form the seam or seal with the material. Alternatively, and without using a thermoset adhesive, hot air can be used to apply heat to the contact area or path along the thermoplastic, elastomeric, or similar material to melt the contact area or path for later fusion to form the seam or seal.
Heat sealing is in wide spread use. For example, it is used to weld electronics components and medical test devices. Heat sealing is also used to seal laminate foils and films to medical devices, such as, trays, bottles, and containers, to prevent contamination of such devices. In the medical and food industries, heat sealing is used to manufacture bags and other flexible containers. Heat sealing is also used to weld the perimeter of thermoplastic materials to form bags and/or for sealing ports and tubes into the bags.
Heat sealing can be used to weld sheets or films of thermoplastic material together with lap seams and other types of seams to form larger pieces of material. It is also used to form single-fold and double fold edge seams along pieces of material. For example, U.S. Pat. No. 4,737,213 teaches a heat sealing process for joining thermoplastic sheets together with lap seams. The process involves directing hot air through several discharge orifices of a nozzle against overlapping upper and lower thermoplastic membranes. The hot air heats contact surfaces of the membrane to its fusion temperature. Then, pressure is applied to the overlapping membranes along the contact surface to join the seam and to create larger sheets of water-resistant membranes for architectural applications. Another method taught by U.S. Pat. No. 6,250,048 uses heat sealing to form tube stock from polyethylene film. A hot air dispenser delivers hot air through a plurality of hot air discharge jets to form a lap seal along overlapping edges of the material, which are then fused along the lap seal to form the tube stock. The tube stock can then be formed into bags with a form-fill-seal machine. Finally, U.S. Patent Application Publication No. 20110083803 teaches a welding machine that uses a hot air nozzle, a hot wedge, or other welding device to join thermoplastic material with a lap seam. The larger pieces of material can be used to manufacture tarps, awnings, tents, and inflatables.
Heat sealing with air delivery techniques has specific applications in bag forming and sealing operations. In an example disclosed in U.S. Pat. No. 3,286,433, a horizontal bag top sealing machine is used to seal filled bags. Positioned within the sealing machine are opposing slots used to direct hot air transversely and inwardly toward an unfolded bag top as the machine passes the bag top horizontally between the opposing slots. The slots are elongated horizontally along the entire length of opposing plenum chambers used to deliver the hot air through the elongated slots. The hot air forms a heat seal bead across the bag top. Similarly, U.S. Pat. No. 5,184,447 teaches using hot air to seal a bag top passing by pairs of nozzles that are positioned in a manner that the nozzles direct air against external sides of the sealing area of the bag top as the bag passes by the nozzles. In this system, hot air impinges on the sealing area to active a heat sealable material used to seal the bag. Finally, U.S. Pat. No. 6,170,238 teaches sealing bag lips with hot air directed through elongated slots against the bag lips as they pass by the elongated slots.
Horizontal fill, fold, and seal machines use heating sealing to seal folded tops of pre-filled bags. A horizontal fill, fold and seal machine performs several continuous steps. It first fills a bag with content, and then, as the filled bag is passed along the machine, a folding apparatus folds the open bag top over into a u-shaped arch. Next, the machine heat seals the folded bag top by directing hot air along the underside portion of the u-shaped arch to heat the bag to a fusion temperature while the bag top passes horizontally by and downstream from the hot air delivery mechanism and, thereafter, by compressing the folded bag top to set the seal. The hot air can also be used to activate a thermoset adhesive deposited along an interior surface of the u-shaped arch. In contrast, a vertical fill, fold and seal machine performs similar steps of filling, folding, and sealing, but rather in a vertical process flow.
Various forms of devices have been used to deliver hot air for heat sealing in fill, fold and seal machines. For example, U.S. Pat. No. 3,381,448 teaches a nozzle that is positioned under a bag top folder mechanism and elongated in the direction of movement of a bag through the fill, fold and seal apparatus. The nozzle has a vertical top wall with a plurality of apertures that discharge pressurized, hot air upwardly against the underside portion of the folded bag top as the bag top passes horizontally by and downstream from the nozzle. Similarly U.S. Pat. No. 4,578,924 and U.S. Patent Application Publication No. 20130016926 teach jetting hot air through nozzles upwardly against the underside portion of the folded bag top as the bag top passes the nozzle.
Heat sealing thermoplastic or other material with hot air requires controlling the airstream of hot air discharged against the surface of the thermoplastic material along the path where the seam or seal will be formed. There are at least three critical aspects of heat sealing, namely, (1) temperature of the hot air, (2) the time of exposure of the material, such as thermoplastic material, to the hot air, and (3) the path along the material to which the airstream is delivered.
Two notable problems may generally arise during heat sealing, namely, overheating or under heating at the path along the material in which a seam or seal will be formed with the material. For example, overheating a material, e.g., thermoplastic, elastomeric, or other “meltable” material, can cause it to shrink, shrivel, or form holes along a part(s) of or the entire length of the region of the material where the hot air was directed. Overheating can be caused by any one or more of: (a) inconsistent, non-uniform heat delivered by a hot air nozzle, (b) heating the hot air to too high a temperature, and/or (c) exposing the material to hot air for too much time. In contrast, under heating prevents a material from being uniformly heated to a fusion temperature along all or portions of the intended path of formation of the seal or seam. In either case, the resulting seal or seam may be partially formed, uneven and/or weak. In either case, the seam or seal is susceptible to breakage or failure due to physical stresses placed on the seal or seam, leakage of contents contained by the seam, and/or intrusion of air, liquids, solids, or vermin or insects from outside the seam.
Prior art air nozzles tend to significantly contribute to turbulent air flow dynamics external to the nozzle that cause inconsistent airflow and uneven heat transfer. With prior art nozzles, heated air rapidly exits apertures, holes or slots and then turbulently mixes with the air external to the nozzle. This creates an asymmetrical and inconsistent air flow pattern jetting from prior art nozzles. Without being bound by any air flow dynamics theory, the air turbulence is exacerbated especially if a nozzle has numerous apertures, holes or slots, such as the prior art nozzle illustrated in FIG. 1. In this figure, the plurality of holes in the prior art nozzle direct airflow in multiple airstreams S with overlapping eddies E that create a swirling turbulence of hot air next to dead spots D adjacent the nozzle and the multiple airstreams S. The eddies E tend to lack consistent heated airflow and the dead spots D generally contain no heated airflow except that which may bleed back into the dead spots D. The eddies E and dead spots D provide inconsistent, asymmetrical airflow patterns external to the nozzle that unevenly heat the material to be sealed and, consequently, create some weak and inconsistent seals.
Indeed, the prior art heat sealing processes and apparatus suffer from hot air delivery devices, such as nozzles and the like, having slots, pluralities of holes or other communications that: (i) discharge an asymmetric, variable airstream pattern(s), as shown, for example in FIG. 1, (ii) unevenly transfer heat to thermoplastic or other material being heat sealed, and consequently (iii) create partially formed, uneven, and/or weak seams or seals in a thermoplastic material or other material, as well as incomplete barriers to leakage and/or intrusion.
Therefore, there is a present need for an improved hot air nozzle, as well as processes and systems of use thereof, that can: (1) discharge a more symmetric or precise airstream pattern for use in heat sealing shown, for example, in FIG. 2; (2) provide a more even heat transfer to material to be sealed or seamed in a heat sealing operation; (3) create a more uniform weld along a desired location for a seam or seal of a material; (4) create a seam or seal with a more even seal strength across the face of a seal or seam of the material; (5) create a barrier to prevent or reduce: (a) leakage of content that may be sealed in a bag or other container formed by heat sealing and/or (b) intrusion of air, water, and/or solids and/or vermin or insects through the seam or seal, such as, particularly with regard to sealed bags and/or containers used for medical applications and food containment and transport; and (6) be easily integrated into: (a) bag top sealing operations performed by fill, fold and seal machines, (b) bag forming operations performed by form, fill, and seal machines, and (c) seaming or sealing operations performed by seam sealer machines.